Interphalangeal joint implant methods and apparatus

ABSTRACT

A method and apparatus for correcting malformed joints, in particular the “hammer toe” contraction of the proximal interphalangeal joint. The disclosure comprises a two-component implant: a proximal phalanx component and a middle phalanx component. An endosseous stem on each component is inserted axially into the end of a respective host bone and, after insertion, the components are attached. The attached components are held together in various ways, for example a detent arm/aperture mechanism. Each component can be cannulated to allow for the passage of a kirschner wire, if necessary, to stabilize adjacent joints such as the proximal interphalangeal joint. The bones of the treated joint can be set to form a desired angle by adjusting the angle formed by the corresponding endosseous stems.

BACKGROUND OF THE INVENTION

This disclosure relates to a method and apparatus for correctingabnormal flexion of the joints of the human foot. More particularly,this disclosure relates to a combination of dorsifexion of themetatarsal/proximal phalangeal joint and plantar flexion of the proximalinterphalangeal joint, commonly called a hammer toe.

The lesser toes of the human foot are composed of three bones andcontain two joints. The three toe bones are a proximal phalanx (closestto the metatarsal bone), a middle phalanx, and a distal phalanx (at theend of the toe). The three toe bones are connected by two toe joints, aproximal interphalangeal joint (PIPJ), which is formed by a distal endof the proximal phalanx and a proximal portion of the middle phalanx;and a distal interphalangeal joint (DIPJ), distal to the PIPJ and formedby a distal end of the middle phalanx and a proximal end of the distalphalanx.

Contraction of the lesser toes of the foot is a common pathologiccondition due to an imbalance between the tendons on the top and bottomof the toe(s). When an affected toe is able to be straightened outmanually, i.e. by an individual or an eternal force, it is referred toas a flexible hammer toe. If left untreated these flexible contractureswill become a fixed deformity know as a rigid hammer toe, which cannotbe put back into normal alignment. The PIPJ is more implicated in ahammer toe syndrome deformity then the DIPJ.

There are many palliative modalities such as pads and various forms oforthodigital devices used to accommodate toe deformities. Thoseconservative options, however, do not provide an individual with enoughcomfort and in some cases are simply illogical given the fact thatvarious alternative surgical options are available.

Throughout the history of performing toe surgery many methods have beenattempted by surgeons ranging from simple tendon release, partial jointexcision, full joint excision and, as a final resort, complete fusion(arthrodesis) of a joint rendering a straight toe. Arthrodesis of thejoint is usually reserved for severe deformities or in cases whereprevious non-arthrodesic procedures were performed but failed to providea patient with desired expectations.

In the past some surgeons fused the PIPJ joint by a simple end-to-endmethod. In this procedure a surgeon resects the articular cartilage ofthe end of one toe bone and the base of an adjoining bone which forms anabnormal joint. The two ends are approximated to each other with theexpectation that they will fuse together. An inherent problem with thismethod is a high rate of non-union with possible recurrence ofdeformity.

Another method is to insert a smooth pin or wire that extends out of thedistal end of the toe. The wire is used to hold the ends of the bones inalignment until fusion occurs. Because these wires and pins are smooth,however, it is possible for the joint to distract leading to a failureor non-union.

Additionally, yet another method was developed which utilized a thinscrew inserted from the tip of a toe across the joint. The purpose ofthis device was to provide compression which facilitates end-to-endfusion. The insertion of a specialized screw is difficult to perform andpresents a possibility of damaging the DIPJ. Furthermore, when the pinis removed it requires a second surgical procedure.

Yet, another device was developed utilizing “memory” metal that wassimply inserted into either the DIPJ or PIPJ after resection of thejoint. These devices are relatively expensive when compared to pins,wires, or screws and also have been known to sometimes expand tooquickly rending the device ineffective.

Finally, a hinged toe fusion device was developed to replace the PIPJ.Each end of the device was inserted into a corresponding end of thebones flanking the PIPJ. A limitation with this device is that it isrelatively difficult to work with. The two components are not designedto be easily separated. Also, the device can be difficult to properlyalign and can rotate out of the proper position after insertion. Also,it does not allow for the additional use of a pin or wire to be insertedacross the metatarsophalangeal joint (MPJ), the joint proximal to thePIPJ, which is sometimes desirable.

The difficulties and limitations suggested in the preceding are notintended to be exhaustive, but rather are among many which demonstratethat although significant attention has been devoted to surgicallycorrecting hammer toe disfigurement, nevertheless surgical implants andprocedures appearing in the past will admit to worthwhile improvement.

BRIEF SUMMARY OF PREFERRED EMBODIMENTS

The subject disclosure includes advantages of bone fusion whilesimplifying the procedure and decreasing or eliminating incidences ofnon-union and non-alignment. A preferred embodiment comprises atwo-component device including (1) a proximal phalanx component and (2)a middle phalanx component. The two components are handled separatelyduring a surgical procedure. Each is inserted axially into a respectivehost bone. After insertion, the components are joined. The attachedcomponents are held together in various ways, for example a detentarm/aperture mechanism. As the components are brought together, the armsof one component slide into a central channel, or cannula, in the othercomponent. The arms are spring loaded as they first encounter an innersurface of the cannula and then spring out when the arms encounterlateral apertures present further on along the cannula. Each componentcan be cannulated to allow for the passage of a wire, e.g. 0.045 inchkirschner wire (k-wire), which passes through the center to stabilizeeither the DIPJ or the MPJ.

An interphalangeal joint implant is inserted using the followingprocedure. A surgeon exposes the PIPJ, separates the two bones making upthe joint and then removes the articular cartilage. Next, a device, suchas a trephine, is used to “core” the ends of the bones on each side ofthe joint. The trephine removes a central cylindrical section of bonewithin the bone shafts which allows for a press-fit junction of thestems of the opposing implant components. A stem of the proximal implantcomponent is inserted into the proximal phalanx and a stem of a distalimplant component is inserted into the middle phalanx. These endosseousstems preferably are non-cylindrical in shape. This will inhibitunintended rotation of the implant after insertion. If stabilization ofan adjacent joint is required a k-wire can be directed from within thejoint out through the tip of the toe making certain that the proximalend of the wire will not prevent the fastening together of the twoimplant components. The middle phalanx portion would then be fitted tothe proximal phalanx portion and then the k-wire can be passed throughthe MPJ.

THE DRAWINGS

Numerous advantages of the present disclosure will become apparent fromthe following detailed description of preferred embodiments taken inconjunction with the accompanying drawings wherein:

FIG. 1 is an axonometric view of a context of the disclosure comprisinga front portion of a human foot with some flesh removed from a lessersecond toe to illustrate severe plantar flexion of the proximalinterphalangeal joint (“PIPJ”) reflecting a rigid joint deformitycommonly known as hammer toe;

FIG. 2 is an axonometric view of an interphalangeal joint implant inaccordance with a preferred embodiment of the invention;

FIGS. 3A-3B are axonometric views of individual proximal and distalcomponents of the interphalangeal joint implant depicted in FIG. 2;

FIG. 4 is a cross-sectional view taken along section line 4-4 of FIG. 2;

FIGS. 5A-5B are cross-sectional views taken along sections line 5A-5Aand 5B-5B in FIGS. 3A and 3B, respectively;

FIG. 6 is a cross-sectional view taken along section line 6-6 in FIG. 2;

FIGS. 7A-7B are a side views taken along section lines 7A-7A and 7B-7Bin FIGS. 3A and 3B, respectively;

FIG. 8 is a top view of the interphalangeal implant shown in FIG. 2;

FIG. 9 is a side view of the interphalangeal implant depicted in FIG. 8.

FIG. 10 is a top view of an alternative preferred embodiment of theinterphalangeal implant;

FIG. 11 is a side view of the interphalangeal implant depicted in FIG.10 illustrating one of the endosseous stems with an imaginary centrallongitudinal axis offset from the other stem's axis by a distance “A,”and by an angle Theta (θ); and

FIGS. 12A-E illustrate, in schematic format, a procedure for correctinga misaligned PIPJ (FIG. 12A) where the bones flanking the PIPJ areseparated (FIG. 12B), tissue around the PIPJ is removed (FIG. 12C), theimplant components are inserted, one into each of the bones flanking thePIPJ (FIG. 12D), and the components of the implant are joined into anintegrated unit (FIG. 12E).

DETAILED DESCRIPTION

Context of the Invention

Referring now particularly to the drawings, wherein like referencecharacters refer to like parts, and initially to FIG. 1, there will beseen a schematic illustration of a context of the subject disclosure—amisaligned interphalangeal joint commonly referred to as a “Hammer toe.”

The disclosure is directed to correction of misalignment betweenvirtually any two bones, but particularly for the flange bones that makeup the five digits of the foot and hands. A typical bone misalignment isillustrated in FIG. 1, with flesh removed from a second toe forillustrative purposes. Depicted are a metatarsal 100, proximal phalanx102, middle phalanx 104 and distal phalanx 106 bone segments in a humanfoot. As noted above, FIG. 1 illustrates a hammer toe conditioncharacterized by dorsifexion of the metatarsal/proximal phalangeal joint108 and plantar flexion the proximal interphalangeal joint (“PIPJ”) 110.The subject apparatus and procedure are directed to correction of thisabnormal flexion of the PIPJ. Although the subject disclosure isdirected in particular to medically correcting hammer toe syndrome it isalso useful for more curved or claw toe maladies as well. In this sensethe term hammer toe as used herein includes claw toe, mallet toe andcurly toe conditions. The disclosure also applies to analogousconditions affecting human fingers.

Interphalangeal Joint Implant

FIG. 2 illustrates an axonometric view of the device with two componentparts operably joined together. FIG. 3A is the proximal phalanxcomponent and FIG. 3B is the middle phalanx component of a human secondtoe.

The proximal phalanx component 112, FIG. 3A, is designed to be insertedinto the distal end of the proximal phalanx. It comprises an endosseousstem 114, 116 and a base 118. The stem is either cylindrical,non-cylindrical or a combination of the two. A non-cylindrical shape hasthe advantage that the stem will not easily rotate after insertion intothe proximal phalanx. The component 112 illustrated in FIG. 3A combinesa cylindrical portion 114 at the tip of the stem and a non-cylindrical,oval or regular trapezoidal portion 116 at the base of the stem. Theshape need not be oval or regular trapezoidal. Any shape that isnon-spherical in cross-section will function to inhibit rotation of thedevice once it is inserted into the bone. Other measures can be employedto inhibit or prevent rotation such as the use of adhesives or surgicalcement. Also, the device can be designed to screw into place providedone insures that the device will be in the proper orientation when thebase of the device contacts the end of the bone.

Other structures can be added to the device to inhibit an untendedtendency for the device to loosen or slide out from the end of bone. Forexample, the device can have regular or irregular surface protrusions.Alternatively, the surface of the stem can have various structures andshapes that promote tissue in growth such as interstitial spaces, ribs,channels, holes, grooves and the like.

The proximal phalanx component 126 also contains a base 128. When thecomponent is fully inserted, the base will be flush against the distalend of the proximal phalanx, in position to contact the correspondingbase of the middle phalanx component illustrated in FIG. 3B.

The base can be equipped with a registry structure that will insure thebases, FIG. 3A and FIG. 3B, will properly align when brought intocontact. A preferred registry structure is illustrated in FIG. 3A, twopins 120 that interact with correspondingly shaped circular cavities 136in the base 128 of the middle phalanx component illustrated in FIG. 3B.

The middle phalanx component, FIG. 3B, designed for insertion into theproximal end of the middle phalanx, will be generally smaller than theproximal phalanx component of FIG. 3A but is similar in other respects.The middle phalanx component will have an endosseous stem 130 and a base128. The stem can be either cylindrical, non-cylindrical or acombination of the two, just as its counterpart in FIG. 3A. The stemillustrated in FIG. 3B has a non-cylindrical, oval shape 130.

The middle phalanx component, like its proximal phalanx counterpart, canhave additional structures that inhibit (or prevent) the device fromrotating or otherwise loosening after it is inserted into the end of thebone.

When the two components are brought together in correct alignment, alocking mechanism will engage and hold the components together. Apreferred locking mechanism features lateral detent arms on onecomponent and a corresponding aperture on the other component. As thetwo components are slid together the arms are spring loaded then, whenthey encounter apertures on the corresponding component, the arms springout and lock the two components together. An example of this preferredlocking mechanism is seen in FIGS. 4, 5A and 5B, which arecross-sections of FIGS. 2, 3A and 3B respectively. FIG. 5B illustratesdetent arms 132 which have a bulge at the head 134. The arms aredesigned so that they can be compressed into an opening 122 (FIG. 3A) inthe complementary component. Then the arms will spring out when thebulge 134 lines up with the mating aperture 122 in the complementarycomponent. The two components locked together can be seen in FIG. 2 andFIG. 4 which is a cross-section of FIG. 2 taken along line 4.

The locking mechanism can have an additional design function whichallows the two components to properly align and maintain a properalignment. This is illustrated in FIGS. 6, 7A and 7B, which arecross-sections of FIGS. 2, 3A and 3B taken along line 6, 7 a and 7B,respectively. The arms have a taper 132 as shown in FIG. 7B that issized to completely fill a complementary taper on said parallel innersurfaces 124 shown in FIG. 7A. The taper insures proper alignment andprevents rotation of the components after the components are lockedtogether as shown in FIG. 6.

Other structures and mechanical components in addition to the oneillustrated here can perform the function of locking the two componentstogether. These can be differently shaped prongs, flexible links or anyother type of arm or protrusion that extends from one component to theother. The structures can be any male/female pair of mating structurethat, when the pairs contact each other, lock the two componentstogether.

Alternatively, the structure used to lock the components together can beextra elements such as various epoxies, adhesives, magnets or theaddition of a third structure specifically designed for locking, such asa clip. This third structure would be moved into position and interactwith structures on both pieces and keep them together. Of course anycommon locking mechanism will function with this device such as screws,pins, rivets, nuts and bolts and the like. A preferred locking structureis a detent arm/aperture mechanism.

Under certain conditions it may become desirable to remove the implantor merely separate the two components after they have been joined. Forthis purpose a separation notch 119/129 is provided as shown in FIG. 2.The notch is shown in the separated components 119, 129 in FIGS. 3A and3B. The surgeon can insert into the notch a surgical tool that createsleverage and mechanical advantage allowing the surgeon to pry apart thetwo components.

The purpose of the implants is to treat bones in an abnormal andsometimes dysfunctional position, such as a hammer toe, and toreestablish function. The bones must function properly throughout activemotion of the foot as well as when the foot is at rest. To a firstapproximation, the functional position is to straighten the PIPJ joint,that is, the longitudinal axis of the proximal phalanx is in axialalignment with the longitudinal axis of the middle phalanx. This maynot, in practice, be the optimal position for the PIPJ joint. In anotherpreferred embodiment, a slight angle between these bones may be morefunctional for a patient. In this case the implants can be altered sothat the PIPJ varies from straight to 15° from linear. A preferableangle is 10° from linear. These embodiments are illustrated in FIGS. 8through 11. FIGS. 8 and 9 illustrate a device designed to produce aperfectly straight (0° angle) PIPJ joint. FIG. 8 is a top view of thedevice. FIG. 9 is a side view. Compare these to FIGS. 10 and 11, whichillustrate a device in which the PIPJ joint will be offset fromperfectly straight by the angle “θ” which, in this example, is 10°. FIG.10 is a top view and FIG. 11 is a side view.

Notice that the middle phalanx component 218 in FIG. 11 is offset fromthe proximal phalanx component 210, 212 by a distance of “A.” Thisoffset is provided to deal with an issue arising from cannulation of thedevice. When the device is straight, that is, designed to generate a 0°angle for the PIPJ joint, a cannulation will pass straight down thecentral axis of both components of the device. The cannulation willenter at the proximal end of the proximal phalanx component and exit outthe distal end of the middle phalanx component. When, however, thedevice is angled a cannulation entering at the proximal end of theproximal phalanx component may exit out the side of the middle phalanxcomponent, rather than the end.

This problem is resolved as shown in FIG. 11. An offset will allow thecannulation to continue straight through the middle phalanx componentand exit out the end. In FIG. 11 the central longitudinal axis of theproximal phalanx component is shown. Note that this axis is extendeddown the length of the middle phalanx component 218 and exits throughthe end of the middle phalanx component. This is because the middlephalanx component is offset dorsally (in FIG. 11 this is to the left) bythe distance “A.” If the middle phalanx component were not dorsallyoffset, the central axis line would exit on the dorsal (left) side ofthe middle phalanx component rather than out the end, as shown. Thus,this offset allows a straight cannulation to pass from one end of thetwo component device to the other, even if the central axes of the twocomponents are not collinear.

While a preferred embodiment of the device is use in the PIPJ to correcthammer toe, the device is not limited solely to use with the lesser toesbut can also be used in fingers as well as the thumb and great toe.Indeed, variations of the device can treat a wide variety of maladiesrelated to improper bone alignment. A non-exhaustive list of examplesincludes: flexible and rigid hammer toe, deviated/crooked toes orfingers (caused by either physical injury or inherited) arthriticjoints, claw toe, mallet toe and long toes requiring shortening (e.g.Morton's Toe).

A preferred material for the implant is medical grade titanium. However,other medical grade materials can also be used.

Method of Treatment for Abnormal Flexion

As discussed previously, hammer toe malady consists of a combination ofdorsifexion of the metatarsal/proximal phalangeal joint 108 (FIG. 1) andplantar flexion of the PIPJ 110 (FIGS. 1, 12A). It is treated bycorrecting the PIPJ 110 misalignment, as illustrated in FIG. 1 and FIGS.12A-12E. FIGS. 12A-E illustrate the bones flanking the PIPJ inisolation. This series of figures outline a preferred method of use ofthe interphalangeal joint implant in which the PIPJ 110 is targeted forcorrection. In a typical operation, an excision is made to expose anarea surrounding the PIPJ 110, the distal end of proximal phalanx 102and the proximal end of the middle phalanx 104. These bones are thenseparated, as shown in FIG. 12B, and the articular cartilage on eitherside of the joint is removed. If the ends of the bones 300, 304 aremalformed or damaged the ends of the bones may be osteotomized to createa proper surface for the next step in the procedure as shown in FIG.12C.

Next, central shafts 302, 306 are introduced into the ends of the bonesusing standard methods. For example, the ends of the two bones can be“cored” using a trephine, a cylindrical drill with a hollow center. Thespecifics of the operation are surgeon's choice. For example, to preventproblematic “drift” of the trephine as the teeth first contact the bone,a pilot hole can be drilled first. A trephine with a central drill guideis used as drill guide is inserted into the pilot hole. As long as thedrill guide remains in the guide hole, the trephine will remain centeredat the proper location during the drilling operation.

After the ends of the bones 300, 304 are cored to form a central channelto the desired depth 302, 306 the two components of the implants 112,126 are inserted into the bones as shown in FIG. 12D. A proximal phalanxcomponent 112 is designed for insertion into the distal end 300 of theproximal phalanx 102 and a middle phalanx component 126 is designed forinsertion into the proximal end 304 of the middle phalanx 104.

The surgeon should drill the channels so that they form a tight fit withthe inserts. If there is any doubt the surgeon should err on the side ofdrilling a channel that is slightly too large. After insertion, tissueingrowth can, so some extent, fill in and replace the missing bonetissue to produce a lasting phalangeal joint connection.

The distal interphalangeal joint (DIPJ) 111, the joint between themiddle phalanx and the distal phalanx, can also be affected by bonemisalignment and require stabilization. In this case Kirschner wire(k-wire) is employed. K-wire is directed from within the PIPJ outthrough the tip of the toe making certain that the proximal end of thewire will not prevent the fastening together of the two implantcomponents. When properly installed, k-wire passes through the center ofthe implant, the middle phalanx and the distal phalanx. The k-wiretypically exits the distal end of the distal phalanx. When installed inthis manner, the k-wire in combination with the implant will stabilizethe DIPJ 111 as well as the PIPJ 110.

The method functions by restoring a preferred angle, θ, between thecentral axis of the proximal phalanx and the central axis of the middlephalanx. The angle θ is defined as the degree by which the imaginarycentral axis of the middle phalanx stem is pointed downward with respectto the imaginary central axis of the proximal phalanx. In one preferredembodiment θ is zero, that is, the two bones are aligned linearly. Inanother embodiment θ can be any angle between zero and approximatelyfifteen degrees. In a preferred embodiment θ is approximately tendegrees.

The preferred angles above will be achieved by designing theinterphalangeal joint implant so that these same angles are presentbetween the corresponding parts of the implant. The imaginary centralaxises of the middle phalanx stem and that of the proximal phalanx stemwill form the angle θ.

In the specification and claims the expression “approximately” or“generally” are intended to mean at or near, and not exactly, such thatthe exact location or configuration is not considered critical unlessspecifically stated.

In the claims in some instances reference has been made to use of theterm “means” followed by a statement of function. When that conventionis used applicant intends the means to include the specific structuralcomponents recited in the specification, including the drawings, and inaddition other structures and components that will be recognized bythose of skill in the art as equivalent structures for performing therecited function and not merely structural equivalents of the structuresas specifically shown and described in the drawings and writtenspecification. The term “attachment” is intended to mean the physicalstructure disclosed in the specification and also other designs toperform a permanent or reversible connection function such as forexample surgical cement, screws, clips, detents, and other attachmentstructures.

In describing the invention, reference has been made to preferredembodiments. Those skilled in the art however, and familiar with thedisclosure of the subject invention, may recognize additions, deletions,substitutions, modifications and/or other changes which will fall withinthe scope of the invention as defined in the following claims.

What is claimed is:
 1. An interphalangeal joint implant for correctionof abnormal flexion of a lesser human toe by insertion at a proximalinterphalangeal joint between a distal end of a proximal phalanx and aproximal end of a corresponding middle phalanx, said interphalangealjoint implant comprising: a proximal phalanx component comprising afirst base plate, a central longitudinal cannulation, and a proximalphalanx stem mounted upon said first base plate and being operable forinsertion into an interior portion of a distal end of a proximalphalanx; a middle phalanx component comprising a second base plate, acentral longitudinal cannulation, and a middle phalanx stem mounted uponsaid second base plate and being operable for insertion into an interiorportion of a proximal end of a middle phalanx; and an attachment forjoining said first base plate to said second base plate to maintain adesired angle between a proximal phalanx and a middle phalanx bone andthus correcting abnormal flexion of a lesser human toe, wherein saidproximal phalanx stem comprises a cylindrical portion at the tip of saidproximal phalanx stem; and a generally trapezoidal portion havinggenerally arcuate sides, joined to said first base plate and extendingto the cylindrical portion of said proximal phalanx stem, wherein saidfirst base plate and said second base plate include complementary maleand female registry structures configured to insure the base plates willproperly align when brought into contact, wherein said attachmentcomprises: two parallel detent arms integrally connected to andextending from the middle phalanx component, each arm comprising a flatouter surface and a distal bulge; and two flat parallel inner surfacesformed on the central longitudinal cannulation of the proximal phalanxcomponent and configured to interact with the flat outer surfaces forproper orientation of the two components, the inner surfaces comprisingtwo opposing through-apertures fashioned through the proximal phalanxcomponent, wherein said two parallel detent arms are spring loaded wheninserted into the central longitudinal cannulation of the proximalphalanx component; and wherein said two parallel detent arms lock whentheir distal bulges reach the through-apertures in the proximal phalanxcomponent.
 2. An interphalangeal joint implant as defined in claim 1wherein said attachment further comprises: said parallel detent armshaving a taper that is sized to completely fill a complementary taper onsaid parallel inner surfaces wherein said taper prevents rotation of thecomponents after attachment.
 3. An interphalangeal joint implant asdefined in claim 1 wherein: said implant further comprises surfacestructures that allow for tissue ingrowth.
 4. An interphalangeal jointimplant as defined in claim 3 wherein: said surface structures areselected from the group consisting of interstitial spaces, ribs,channels, holes and grooves.
 5. An interphalangeal joint implant asdefined in claim 1 wherein said registry structures further comprise:said male registry structure is a pin extending from one of the baseplates and said female registry structure is a complementary hole in theother base plate.
 6. An interphalangeal joint implant as defined inclaim 1 further comprising: said desired angle is maintained by havingan imaginary central longitudinal axis of said proximal phalanx stembeing coaxial with an imaginary central longitudinal axis of said middlephalanx stem.
 7. An interphalangeal joint implant as defined in claim 1further comprising: said desired angle is maintained by having animaginary central longitudinal axis of said middle phalanx stem offsetby a patient preferred angle θ with respect to an imaginary centrallongitudinal axis of said proximal phalanx stem, wherein angle θ iswithin the range of 0° to 15°.
 8. An interphalangeal joint implant asdefined in claim 7 wherein angle θ is approximately 10°.